An atomistic introduction to anisotropic etching

This review-oriented paper presents a simplified model of anisotropic etching of crystalline silicon for the three principal orientations (111), (110) and (100), including their vicinal surfaces. The model combines pit nucleation and step flow with micromasking and diffusion phenomena in order to explain the major morphologic features and their changes with concentration. It also qualitatively explains the orientation and concentration dependence of the etch rate. We conclude that the shallow round pits on (100) and the elongated zigzag structures on (110), each of which constitutes the basic morphology of the corresponding surface, are actually the result of the same physical phenomenon, diffusion, disguised by a different underlying symmetry. It is also shown that the formation of hillocks on the two surfaces at different concentrations is a related process. We also describe and support the idea that the rotation of the triangular pits on (111) is due to a selective blocking mechanism by the etchant cations and explain how the formation of polygonal steps and/or step bunches on miscut (111) surfaces can occur as a result of diffusion phenomena and not only due to micromasking. Finally, the particular features of Cu as a micromasking agent are explained.